[muscript] Slightly better debugging experience

muscript/src/main/java/io/gitlab/jfronny/muscript/compiler/Error.java

@@ -3,9 +3,29 @@ package io.gitlab.jfronny.muscript.compiler;
 /**
  * Class for storing errors produced while parsing.
  */
-public record Error(int line, int character, char ch, String message) {
+public record Error(String source, int character, String message) {
     @Override
     public String toString() {
-        return String.format("[line %d, character %d] at '%s': %s", line, character, ch, message);
+        StringBuilder builder = new StringBuilder();
+        if (character >= source.length()) {
+            builder.append("Error at character ").append(character);
+        }
+        else {
+            builder.append("Error at '").append(source.charAt(character)).append("' (character ").append(character).append(")");
+        }
+        builder.append(": ").append(message);
+
+        int lineStart = source.lastIndexOf('\n', character);
+        int lineEnd = source.indexOf('\n', character);
+        if (lineEnd == -1) lineEnd = source.length();
+
+        String line = source.substring(lineStart + 1, lineEnd);
+        int lineNumber = lineStart > 0 ? (int) source.substring(0, lineStart).chars().filter(c -> c == '\n').count() : 1;
+
+        String linePrefix = String.format("%1$6d", lineNumber) + " | ";
+
+        builder.append('\n').append(linePrefix).append(line);
+        builder.append('\n').append(" ".repeat(linePrefix.length() + (character - lineStart - 1))).append("^-- Here");
+        return builder.toString();
     }
 }

muscript/src/main/java/io/gitlab/jfronny/muscript/compiler/Lexer.java

@@ -7,11 +7,10 @@ public class Lexer {
     /** The string representation of the token */
     public String lexeme;
 
-    public int line = 1, character = -1;
     public char ch;
 
-    private final String source;
+    public final String source;
-    private int start, current;
+    public int start, current;
 
     public Lexer(String source) {
         this.source = source;
@@ -35,8 +34,8 @@ public class Lexer {
 
         char c = advance();
 
-        if (isDigit(c) || (c == '-' && isDigit(peek()))) number();
+        if (isDigit(c)) number();
-        else if (isAlpha(c)) identifier();
+        else if (isIdentifier(c)) identifier();
         else {
             switch (c) {
                 case '\'', '"' -> string(c);
@@ -72,7 +71,6 @@ public class Lexer {
 
     private void string(char stringChar) {
         while (!isAtEnd() && peek() != stringChar) {
-            if (peek() == '\n') line++;
             advance();
         }
 
@@ -100,7 +98,7 @@ public class Lexer {
     private void identifier() {
         while (!isAtEnd()) {
             char c = peek();
-            if (isAlpha(c) || isDigit(c)) {
+            if (isIdentifier(c) || isDigit(c)) {
                 advance();
             } else if (c == ':' && peekNext() == ':') {
                 advance();
@@ -123,11 +121,7 @@ public class Lexer {
             char c = peek();
 
             switch (c) {
-                case ' ', '\r', '\t' -> advance();
+                case ' ', '\r', '\t', '\n' -> advance();
-                case '\n' -> {
-                    line++;
-                    advance();
-                }
                 default -> {
                     start = current;
                     return;
@@ -139,7 +133,7 @@ public class Lexer {
     // Helpers
 
     private void unexpected() {
-        createToken(Token.Error, "Unexpected character.");
+        createToken(Token.Error, "Unexpected character");
     }
 
     private void createToken(Token token, String lexeme) {
@@ -160,7 +154,6 @@ public class Lexer {
     }
 
     private char advance() {
-        character++;
         return ch = source.charAt(current++);
     }
 
@@ -182,7 +175,7 @@ public class Lexer {
         return c >= '0' && c <= '9';
     }
 
-    private boolean isAlpha(char c) {
+    private boolean isIdentifier(char c) {
         return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' || c == '$';
     }
 }

muscript/src/main/java/io/gitlab/jfronny/muscript/compiler/Parser.java

@@ -230,7 +230,7 @@ public class Parser {
 
     // Helpers
     private ParseException error(String message) {
-        return new ParseException(new Error(current.line, current.character, current.ch, message));
+        return new ParseException(new Error(lexer.source, current.current - 1, message));
     }
 
     private TokenData consume(Token token, String message) {
@@ -258,7 +258,7 @@ public class Parser {
         previous.set(current);
 
         lexer.next();
-        current.set(lexer.token, lexer.lexeme, lexer.line, lexer.character, lexer.ch);
+        current.set(lexer.token, lexer.lexeme, lexer.start, lexer.current, lexer.ch);
 
         if (current.token == Token.Error) {
             throw error(current.lexeme);
@@ -275,19 +275,19 @@ public class Parser {
     private static class TokenData {
         public Token token;
         public String lexeme;
-        public int line, character;
+        public int start, current;
         public char ch;
 
-        public void set(Token token, String lexeme, int line, int character, char ch) {
+        public void set(Token token, String lexeme, int start, int current, char ch) {
             this.token = token;
             this.lexeme = lexeme;
-            this.line = line;
+            this.start = start;
-            this.character = character;
+            this.current = current;
             this.ch = ch;
         }
 
         public void set(TokenData data) {
-            set(data.token, data.lexeme, data.line, data.character, data.ch);
+            set(data.token, data.lexeme, data.start, data.current, data.ch);
         }
 
         @Override

muscript/src/test/java/io/gitlab/jfronny/muscript/test/ErrorTest.java

@@ -0,0 +1,27 @@
+package io.gitlab.jfronny.muscript.test;
+
+import io.gitlab.jfronny.muscript.compiler.*;
+import org.junit.jupiter.api.*;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class ErrorTest {
+    @Test
+    void invalidCode() {
+        assertEquals("""
+                Error at 'e' (character 8): Expected number but is Boolean
+                     1 | 15 + true
+                                 ^-- Here""",
+                assertThrows(Parser.ParseException.class, () -> Parser.parse("15 + true")).error.toString());
+        assertEquals("""
+                Error at ''' (character 9): Expected number but is String
+                     1 | 15 + 'yes'
+                                  ^-- Here""",
+                assertThrows(Parser.ParseException.class, () -> Parser.parse("15 + 'yes'")).error.toString());
+        assertEquals("""
+                Error at '=' (character 7): Unexpected character
+                     1 | string = 'Value'
+                                ^-- Here""",
+                assertThrows(Parser.ParseException.class, () -> Parser.parse("string = 'Value'")).error.toString());
+    }
+}

muscript/src/test/java/io/gitlab/jfronny/muscript/test/StringTest.java

@@ -1,6 +1,5 @@
 package io.gitlab.jfronny.muscript.test;
 
-import io.gitlab.jfronny.muscript.compiler.*;
 import org.junit.jupiter.api.*;
 
 import static io.gitlab.jfronny.muscript.test.MuTestUtil.*;
@@ -15,11 +14,4 @@ public class StringTest {
         assertTrue(bool("string == 'Value'"));
         assertFalse(bool("string == 'Something else'"));
     }
-
-    @Test
-    void invalidCode() {
-        assertThrows(Parser.ParseException.class, () -> Parser.parse("15 + true"));
-        assertThrows(Parser.ParseException.class, () -> Parser.parse("15 + true"));
-        assertThrows(Parser.ParseException.class, () -> Parser.parse("string = 'Value'"));
-    }
 }